Per gmtime manpage, tm_mon is the number of months since January

Per gmtime manpage, tm_mon is the number of months since January
while MonthNo is the month of the year, so tm_mon should be MonthNo-1.

Similarly, tm_mday is the day of the month, and DayNo is the number
of days since the first day of the month. Assigning DayNo+1 to
tm_mday to fit the definition.

This commit also corrected miscalculated MonthNo and DayNo for the
first day of the month. (Thanks to Laszlo Ersek!)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Long Qin <qin.long@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14481 6f19259b-4bc3-4df7-8a09-765794883524